A cryogenic filter assembly is described in U.S. Pat. No. 6,212,404. This reference broadly refers to a wireless communication system comprising a tower having one or more antennas coupled to a module which includes a bandpass wave guide cavity filter and a low noise amplifier, which module is connected to receiver circuitry via one or more co-axial cables. The cavity filter is shown coupled to cryogenic cooling apparatus comprising a heat exchange unit and a cooling generation unit. U.S. Pat. No. 6,212,404 also discloses retro-fitting of conventional rural antenna configurations comprising a tower having one or more antennas and connected to an RX filter and low noise amplifier as well as a TX filter wherein cryogenic cooling apparatus is fitted to the RX filter and/or the low noise amplifier. The use of the cryogenic cooling apparatus is stated to substantially increase the sensitivity of the wireless communication system and to substantially decrease the noise factor. The cryogenic cooling system disclosed in U.S. Pat. No. 6,212,404 comprises a compressor coupled to a heat exchange unit for continuous circulation of a gaseous refrigerant fluid between the compressor and the heat exchange unit. Thus, cooled and compressed fluid is passed into the heat exchange unit through a high pressure line and warm expanded fluid is returned to the compressor from the heat exchange unit through a low pressure line. The heat exchange unit is located in an evacuated chamber which also houses the wave guide cavity filter which is in direct contact with a cooling finger of the heat exchange unit. Thus, in this arrangement, the wave guide cavity filter is in direct contact with the cold head of the cryogenic cooling apparatus and this has resultant disadvantages of providing an unduly complicated refrigeration circuit insofar as structure is concerned with a subsequent loss of operating efficiency.
It is noted, however, that U.S. Pat. No. 6,212,404 only discloses a wave guide cavity filter such as that disclosed in U.S. Pat. No. 5,936,490 and it disclaims the use of filters formed from high temperature super conducting (HTS) materials. Such HTS materials provide an advantage of constructing resonators with very large unloaded Q factor.